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6. PROVENANCE OF THE HP-HT UPPER ALLOCHTHON
118
RESULTS
U–Pb results
U–Pb dating results are given in Tables S1–S5 and
represented in Fig. 3. To allow forward comparisons,
the age spectrum has been divided into four major
groups: Palaeozoic–Neoproterozoic (<1 Ga), Mesopro-
terozoic (1.6–1 Ga), Paleoproterozoic (2.5 –1.6 Ga)
and Archean (>2.5 Ga). Descriptions of U–Pb results
of each sample are as follows.
From sample GCH– 02, 156 analyses were per-
formed, of which 118 were concordant (< 10% discor-
dance, d = 24.4%, d: percentage of discordant
analyses). Of these, 36 are Palaeozoic–Neoproterozoic
(30.5%), 0 are Mesoproterozoic, 51 are Paleoprotero-
zoic (43.2%) and 31 are Archean (26.3%). MDA02
(GCH–02 MDA) calculated for this sample, using 11
ages (see above), is 498.4 5.8 Ma.
From sample GCH– 06, 142 analyses were
performed of which 126 were concordant (<10%
discordance, d = 11.3%). Of these, 28 are Palaeozoic–
Neoproterozoic (22.2%), 0 are Mesoproterozoic, 58
are Paleoproterozoic (46%) and 40 are Archean
(31.7%). MDA 06 calculated for this sample, using
seven ages (see above), is 510.4 3.5 Ma.
From sample GCH–17, 134 analyses were
performed, of which 116 were concordant (<10%
discordance, d = 13.4%). Of these, 73 are Palaeozoic–
Neoproterozoic (62.9%), 6 are Mesoproterozoic
(5.2%), 22 are Paleoproterozoic (19%) and 15 are
Archean (12.9%). MDA17 calculated for this sample,
using 24 ages (see above), is 515.4 2.8 Ma.
From sample GCH–21, 161 analyses were
performed of which 139 were concordant (<10%
discordance, d = 13.7%). Of these, 22 are Palaeozoic–
Neoproterozoic (15.8%), 2 are Mesoproterozoic
(1.4%), 69 are Paleoproterozoic (49.6%) and 46 are
Archean (33.1%). MDA21 calculated for this sample,
using three ages (see above), is 510 28 Ma.
From sample GCH-24, 136 analyses were
performed, of which 114 were concordant (<10%
discordance, d = 16.2%). Of these, 54 are Palaeozoic–
Neoproterozoic (47.4%), 9 are Mesoproterozoic
n = 463
T , model ageDM
Cadomian
0
–55
–45
–35
–25
–15
–5
5
15
25
0 500 1000 1500 2000 2500 3000
εHf(
t)
crust
Eburnean crust
Archean crust
Hadean crust
(Jack Hills trend)
Depleted Mantle
CHUR
Crustal evolution trend176
177
( Lu/ Hf = 0.0113)
BROM 500 1000
1500
2000 2500
3000
GCH-02
GCH-06
GCH-17
GCH-21
GCH-24
Cadomian crust
Eburnean crust
Archean crust
Hadean crust
500
–55
–45
–35
–25
–15
–5
5
15
25
400 500 600 700 800 900
εHf(
t)
U–Pb age (Ma)
U–Pb age (Ma)
T , model ageDM
176 177 ( Lu/ Hf = 0.0113)
DM
CHUR
700 600 800 900
n= 177
Crustal evolution trend
GCH-02
GCH-06
GCH-17
GCH-21
GCH-24
(a)
(b)
Fig. 7. Hf isotope evolution diagram
showing Banded Gneisses combined U–Pb
and Lu–Hf zircon data. Error bars are 2r.
Oblique coloured bands represent crustal
evolution trends for Hadean, Archean,
Eburnean and Cadomian DM derived
rocks. Adaptive Kernel Density Estimation
of analysed zircon with Lu–Hf systematics
is represented in grey (a) Hf isotope
evolution diagram of all analysed zircon
grains (complete aKDEs were built with
bandwidth = 15 Ma and histograms with
binwidth = 25 Ma). (b) Hf isotope
evolution diagram of analysed zircon grains
in the age range of 1000–400 Ma (partial
aKDEs were built with bandwidth = 15 Ma
and histograms with binwidth = 5 Ma;
DensityPlotter5.0 software; Vermeesch,
2012). See text for discussion and for
constants and parameters used. CHUR,
chondritic uniform reservoir; DM, depleted
mantle; MORB, mid ocean ridge basalt.
© 2015 John Wiley & Sons Ltd
968 R. ALBERT ET AL.